In the rubber industry, it has been hitherto known that when a rubber composition is produced which includes a filler such as carbon black, a wet rubber masterbatch is used to improve the workability of the rubber composition and the dispersibility of the filler. This manner is a manner of mixing the filler and a dispersing solvent with each other beforehand at a predetermined ratio, dispersing the filler into the dispersing solvent by mechanical force, mixing the resultant filler-containing slurry solution with a rubber latex solution in a liquid phase, adding a solidifier such as an acid, after the mixing, to the mixture to solidify the mixture, collecting the solidified product, and then drying the collected product. The use of the wet rubber masterbatch can give a rubber composition better in filler-dispersibility, and rubber properties such as workability and reinforceability than the use of any dry rubber masterbatch, which is yielded by mixing a filler and a rubber with each other in a solid phase. The use of such a rubber composition as a raw material makes it possible to produce, for example, a pneumatic tire decreased in rolling resistance and excellent in fatigue resistance, and such a rubber product.
A process for producing a wet rubber masterbatch indispensably requires a dehydrating step in which from a filler-containing rubber solidified product yielded by mixing at least a filler, a dispersing solvent and a rubber latex solution with each other and then solidifying the mixture, the dispersing solvent, in particular, water is removed. In this dehydrating step, it is general to remove water from the filler-containing rubber solidified product by applying shearing force to the filler-containing rubber solidified product while heating the product by use of a monoaxial extruder or biaxial extruder. However, unless the heating temperature thereof, and others are adjusted, water may not be sufficiently removed, or various properties of the produced wet rubber masterbatch may be deteriorated.
Patent Document 1 listed below describes a producing process in which a dehydrating extruder is used to adjust the proportion of water contained in a masterbatch clam into the range of about 1 to 20% by mass. However, this document neither describes nor suggests conditions for temperature-adjustment before and after the dehydration.